1. Field of Invention
The invention relates to a processing device and method for time domain change of audio and video (A/V) data stream and, in particular, to the processing device and method for performing the time domain change procedure according to the detection of continuous probable times of the SCR domain change.
2. Related Art
There are several A/V compression techniques such as MPEG standard that widely applied for the digital TV and the multimedia applications. The NPEG technique transforms the dynamic A/V data into standard MPEG A/V data stream. That is, the A/V data is recorded in digital format in the storage such as a digital versatile disc (DVD).
The system clock reference (SCR) and the presentation time stamp (PTS) will be add to the packs of the MPEG A/V data stream during the MPEG encoding, and the SCR and the PTS increasing in a fixed rate after the SCR first updated the system time clock (STC). However, when a program is composed by editing and rearranging, the SCR and the PTS will vary such as increasing or decreasing with large amounts suddenly. Since the decoder compares the SCR and the PTS for determining the playing time, and supposes that the STC doesn't change followed the SCR and the PTS varied, the decoder will refer to an old STC and result in the STC asynchronization problem in playing.
In practice, The E-STD model is proposed for solving the STC asynchronization problem. With refer to the FIG. 1, a decoder 10′ decodes many packs of the A/V data stream and outputs a first A/V data, many second A/V data, a first PTS, many second PTS, a first SCR, and many second SCR. A STC counter 14′ initials the first STC with the first SCR such as to the first STC increasing in the fixed rate. An audio data register 16′ and a video data register 18′ temporarily store the first audio data and the first video data transmitted by the decoder 10′ respectively. An audio decoder 20′ and a video decoder 22′ decodes the first audio data and the first video data respectively for generating a first decoded audio data and the first decoded video data during playing. A playing unit 24′ compares the first PTS with the first STC of the first decoded audio data and the first decoded video data, and plays the first decoded audio data and the first decoded video data if the first PTS is equal to the first STC.
The decoder 10′ will send the notice to the audio decoder 20′ and the video decoder 22′ when a domain change of the second SCR happened and detected by the decoder 10′. However, since the data consuming rate of each decoder may not equal to others, the video decoder 22′ probably received the notice later than the audio decoder 20′, and when the audio decoder 20′ starts to consume the data of the second SCR, the video decoder 22′ still consuming the data of the first SCR at the same time. The decoder 10′ therefore sends the second SCR to a subtractor 12′ for calculating the difference of the second SCR and the first SCR, and the subtractor 12′ further generating a second STC through subtracting the difference from the first STC. Hence, a STC counter 14′ receives and forwards the second STC to the audio decoder 20′ for synchronizing the audio decoder 20′ and the video decoder 22′.
Although the E-STD model can be employed as a solution of STC synchronization problem, the decoder may response too late while the SCR domain change happened frequently. For example, time of the SCR domain change is restricted between two video object units (VOUBs) for DVD, or the decoder may response too late while the SCR and the PTS increasing or decreasing with large amounts suddenly and the SCR domain change happened frequently. In addition, the scrape on the disc will result in the faults in referring to the SCR of the A/V data stream.